Nowadays, a dynamic range of a nature scene is greatly beyond a capture capacity of an existing digital equipment. Conventional low dynamic range devices cannot completely cover the dynamic range of a real scene, especially of an extremely dark scene or an extremely bright scene.
Generally, in order to obtain a high dynamic range image by an imaging system with a standard dynamic range, different exposure parameters are used to obtain multiple low dynamic range images of a same static scene, and then the multiple images are combined, in which each low dynamic range image is responsible for collecting different details of the high dynamic scene, an underexposed image mainly records high brightness details of the scene, and an overexposed image is used to record the dark area of the scene.
One method for obtaining the high dynamic range image is as follows. Firstly, a long exposure image (having a large exposure) and a short exposure image (having a small exposure) of the same scene are obtained. Then, the pixel value of each pixel in the long exposure image is combined with the pixel value of each pixel in the short exposure image according to a certain proportion to obtain the pixel value of each pixel in the high dynamic range image. Specifically, the pixel value RESULT of each pixel in the combined image is determined according to RESULT=L*(1−A)+S*A, in which S is the pixel value of each pixel in the short exposure image, L is the pixel value of each pixel in the long exposure image, A is the proportion of the short exposure image and is defined according to A=K*Y_S_AVE/256, where Y_S_AVE is the average brightness value of the short exposure time image, and K is an adjustable value. After processing all the pixels in the images, the high dynamic range image is obtained.
The color of the image obtained by the above method is darker, which is because: a brightness value of the overexposed area of the long exposure image is large, but the long exposure image does not provide any color information; a brightness value of the short exposure image is small, but the short exposure image provides some color information; the brightness value of the combined image is much larger than the brightness value of the short exposure image, but the color information of the combined image is provided by the short exposure image. Therefore, the color value of the combined image is relatively small, which results in that the color of the combined image is dark.